Abstract: The application of wide band-gap power electronic devices with increased voltage and frequency brings more challenges to the insulating packaging technology of silicon-based power electronic systems. Knowing the effect of voltage parameters on insulation performance is helpful to the insulation evaluation for power electronics. In this paper, the effect of repetitive pulse duty cycle on the growth characteristics of electrical trees in epoxy resin was studied. The study show that the shape of electrical trees changes from jungle-like, dense branch-like to sparse branch-like with increasing duty cycles. The length and width of electrical tree increase with increasing duty cycle lower than 10%. While the length and width of the electrical tree decrease with increasing duty cycle higher than 30%, indicating that low duty cycle would enhance the electron injection and accumulation, and thus accelerate electrical tree development. Moreover, the electric field due to shielding effect near the needle tip would suppress electrical tree growth, which results in obvious growth stagnation. The obtained results are expected to provide theoretical and experimental basis for the design of insulation packaging and the improvement of insulation performance of power electronic systems.